1. Field of the Invention
The present invention relates generally to valve gates and, more particularly, to a valve gate assembly for regulating a flow of molten material into a cavity of a mold.
2. Description of the Related Art
Injection molding is a widely known manufacturing process used to produce a variety of parts. Injection molding involves introducing a molten material, for example a molten plastic or resin, into a cavity within a mold until the cavity is filled. The molten material hardens or cures in the mold in the shape of inner surfaces of the cavity. After the molten material hardens or cures, the hardened or cured material is removed from the cavity.
For injection molding, a manifold is typically used for conveying molten material from a central injection portion or sprue to a number of cavities or to multiple points within one large cavity of the mold. An example of such a manifold is disclosed in U.S. Pat. No. 4,964,795 to Tooman. In that patent, a manifold has a passageway through which a molten material may pass. The terminal end of the passsageway, called a gate, is in fluid communication with the cavity of the mold.
In addition, a valve gate is typically used with the manifold to regulate the flow of molten material into the cavity of the mold. An example of such a valve gate is disclosed in U.S. Pat. No. 4,173,448 to Rees et al. In that patent, a valve gate is disposed adjacent the gate and includes a valve rod or pin partially disposed within the passageway that has a terminal end positioned such that it closes the gate and prevents the flow of molten material through the gate. However, the pin can move axially away from the gate and, as it moves farther away from the gate, the flow of the molten material through the gate increases.
It is known to provide an actuator to move the pin of the valve gate. Typically, the actuator is of a pneumatic or hydraulic type. The actuator moves the pin of the valve gate from a fully closed position to a fully open position. In the fully open position, the pin is positioned away from the gate, and molten material flows out the passageway through the gate into the cavity of the mold. When the cavity is full, the pin of the valve gate is moved to the fully closed position, thereby plugging the gate and stopping the flow of the molten material out of the passageway into the mold.
One disadvantage of the above-described valve gates is that the pneumatic actuator requires air valves because air is inconsistent in pressure. Another disadvantage of the valve gates is that the hydraulic actuator may leak oil, which is undesired. Yet another disadvantage of the valve gates is that the pin can only be positioned at the fully open position or at the fully closed position, and cannot be positioned between these two positions. A further disadvantage of the valve gates is that they are relatively slow and not very accurate in positioning of the pin.
Therefore, it is desirable to provide a new valve gate that can be infinitely positioned between a fully opened and fully closed position, providing greater control over the flow of molten material into a mold. It is also desirable to provide a valve gate that has an actuator that eliminates the use of pneumatics or hydraulics. It is further desirable to provide a valve gate that has relatively fast actuation and accurate positioning. Therefore, there is a need in the art to provide a valve gate that meets these desires.